1. Field of the Invention
The present invention relates to a positive resist composition for use in the manufacturing processes of semiconductors such as IC and the like, liquid crystals, the manufacture of circuit substrates for thermal heads and the like, and lithographic processes of other photo-fabrications, and also relates to a pattern-forming method using the same. In particular, the invention relates to a positive resist composition suitable for exposure with an immersion projection exposure apparatus using far ultraviolet rays of wavelengths of 300 nm or less as a light source, and a pattern-forming method using the same.
2. Description of the Related Art
With the progress of fining of semiconductor devices, shortening of the wavelengths of exposure light source and increasing of the numerical aperture of the projection lens (high NA) have advanced and now exposure apparatus of NA 0.84 using an ArF excimer laser having wavelength of 193 nm as a light source have been developed. As generally known, this can be expressed by the following expressions:(Resolution)=k1·(λ/NA)(Depth of focus)=±k2·λ/NA2 wherein λ is the wavelength of exposure light source, NA is the numerical aperture of the projection lens, k1 and k2 are the coefficients concerning the process.
For further higher resolution by the shortening of wavelengths, an exposure apparatus with an F2 excimer laser having wavelength of 157 nm as the light source has been studied, however, the materials of lens for use in the exposure apparatus and the materials of resist are extremely restricted for shortening of wavelengths, so that the realization of the reasonable manufacturing costs of the apparatus and materials and quality stabilization are very difficult, as a result, there are possibilities of missing an exposure apparatus and a resist having sufficient performances and stabilities within a required period of time.
As a technique for increasing resolution in the optical microscope, what is called an immersion method of filling between a projection lens and a sample with a liquid of high refractive index (hereinafter also referred to as “an immersion liquid”) has been conventionally known.
As “the effect of immersion”, the above resolution and depth of focus in the case of immersion can be expressed by the following expressions, taking λ0 as the wavelength of the exposure light in the air, n as the refractive index of immersion liquid to the air, and NA0=sin θ with θ as convergence half angle of the ray of light:(Resolution)=k1·(λ0/n)/NA)0 (Depth of focus)=±k2·(λ0/n)/NA02 
That is, the effect of immersion is equivalent to the case of using exposure wavelength of the wavelength of 1/n. In other words, in the case of the projection optical system of the same NA, the depth of focus can be made n magnifications by immersion. This is effective for every pattern form, and can be combined with super resolution techniques such as a phase shift method and a deformation lighting method.
The apparatus applying this effect to the transfer of micro-fine image pattern of semiconductor device are introduced by JP-A-57-153433, the term “JP-A” as used herein refers to an “unexamined published Japanese patent application” and JP-A-7-220990.
The latest technical advancement of immersion exposure is reported in SPIE Proc., 4688, 11 (2002), J. Vac. Sci. Tecnol. B, 17 (1999), SPIE Proc., 3999, 2 (2000), and WO 2004/077158.
When an ArF excimer laser is used as the light source, it is thought that pure water (refractive index at 193 nm: 1.44) is most promising in the light of the safety in handling, and the transmittance and the refractive index at 193 nm. When an F2 excimer laser is used as the light source, a solution containing fluorine is examined from the balance of the transmittance and the refractive index at 157 nm, but from the viewpoint of environmental safety and in the point of refractive index, a sufficiently satisfactory solution has not been found yet. From the extent of the effect of immersion and the degree of completion of resist, it is thought that immersion exposure technique will be carried on the ArF exposure apparatus earliest.
From the advent of the resist for a KrF excimer laser (248 nm) on, an image-forming method that is called chemical amplification is used as the image-forming method of the resist for compensating for the reduction of sensitivity by light absorption. To explain the image-forming method of positive chemical amplification by example, this is an image-forming method of exposing a resist to decompose an acid generator in the exposed part to thereby generate an acid, utilizing the generated acid as the reactive catalyst to change an alkali-insoluble group to an alkali-soluble group by the bake after exposure (PEB: Post Exposure Bake), and removing the exposed part by alkali development.
The resist for an ArF excimer laser (wavelength: 193 nm) using the chemical amplification mechanism is now being a main current, but there is a drawback that a formed pattern falls down and results in the defect in manufacturing a device, and improvement is required.
When a chemical amplification resist is applied to immersion exposure, it is appointed that since the resist layer inevitably touches an immersion liquid at the time of exposure, the resist layer decomposes and ingredients that adversely influence the immersion liquid ooze from the resist layer. WO 2004/068242 discloses that the resist performance changes by the immersion of a resist for ArF exposure in water before and after exposure and appoints this is a problem in immersion exposure.
Further, when immersion exposure is carried out, there are cases where circular defects called water marks occur on account of the droplets remaining on a resist film after exposure, and improvement is required.